Where do my rendering artifacts come from?
It's due to your camera lens start clipping setting. It's set to 10µm (micro-meter, = 0.001 Blender unit).

For some reason Blender can't render surfaces correctly when the camera's clipping start distance is too low.

Try with some higher value, (e.g. 10cm = 10 Blender unit) and the problem is gone. Select the camera, go to camera tab in properties window, Lens panel: